When you switch on any electrical appliance you will observe some spark in the switch. Do you why spark will occur? Here is the answer….. Air’s dielectric strength is 20Kv/cm. That means when you apply 20Kv voltage between two terminals and the distance between those terminals is 1 cm then dielectric strength of air will be broken between these two terminals and air will behave like conductor. Then you can observe the spark there. In normal house applications the voltage commonly used is 230V. So if the gap between terminals is 0.01cm then in that gap air will conduct for 230V voltage. At that time spark will occur. Please let me know if there are any mistakes in this article.... Please Register or Log in to view the hidden image!